1. Field of the Invention
The present invention relates to a color cathode ray tube apparatus used for a TV, a monitor or the like.
2. Description of Related Art
Nowadays, a so-called self-convergence in-line color cathode ray tube apparatus is in wide use. This color cathode ray tube apparatus includes an in-line electron gun for emitting three aligned electron beams of a center beam and a pair of side beams on both sides of the center beam that pass in the same horizontal plane, a deflection device for generating a pincushion horizontal deflection magnetic field and a barrel vertical deflection magnetic field, and a pair of upper and lower permanent magnets or a pair of upper and lower and a pair of right and left (a set of four) permanent magnets provided at an edge portion of a screen-side opening of the deflection device for assisting these horizontal and vertical deflection magnetic fields. In this color cathode ray tube apparatus, the three electron beams are converged over an entire screen, and the electron gun and the deflection device are combined so that deflection distortion (raster distortion) in upper and lower portions or upper, lower, right and left portions of the screen is corrected to be substantially linear.
In such a self-convergence in-line color cathode ray tube apparatus, the electron gun generally emits the side beams at predetermined angles so as to converge the three electron beams at the center of the screen. The state of convergence of the three electron beams at the center of the screen is adjusted by a CPU (Convergence and Purity Unit) formed of a ring-shaped magnet provided in a neck portion of the color cathode ray tube apparatus.
Conventionally, suggestions have been made to provide the deflection device with various auxiliary devices, thereby improving the shapes of spots of the electron beams on the screen (in the following, simply referred to as the “spots”) while maintaining the convergence characteristics of the three electron beams, and at reducing a variation in the convergence characteristics due to temperature variation. For example, JP 2002-260558 A discloses that, in addition to the above-noted permanent magnets, an auxiliary magnetic field generating device for generating a quadrupole magnetic field 92 shown in FIG. 12 is provided at a position overlapping a horizontal deflection coil in a tube axis direction. In FIG. 12, numeral 91 denotes a magnetic core constituting the deflection device, and numerals 18B, 18G and 18R denote three electron beams. Also, JP 2001-52631A, JP 7(1995)-15736A and JP 2001-126642A disclose that the deflection device is provided with a temperature compensating device in order to reduce the variation in the convergence characteristics due to the temperature variation.
In recent years, there have been increasing demands for a higher quality and a lower cost for a television set using a color cathode ray tube apparatus. Therefore, it has become difficult in terms of cost to add the auxiliary magnetic field generating device so as to achieve a higher quality.
According to the above-described configuration disclosed in JP 2002-260558A, the convergence characteristics and the spot shape improve. However, since a magnetic force of the auxiliary magnetic field generating device varies due to the temperature variation, the convergence characteristics varies, causing a problem of deteriorating image quality. Further, since a pincushion quadrupole magnetic field generated by the auxiliary magnetic field generating device shown in FIG. 12 and a barrel magnetic field generated by a vertical deflection coil cancel each other out, it is difficult to achieve both of the convergence characteristics and the correction of raster distortion. Accordingly, in order to correct the raster distortion, a correction circuit needs to be added to a television set, for example, leading to a problem of the apparatus becoming more complicated and expensive.
In the configurations disclosed by JP 2001-52631A and JP 7(1995)-15736A, although the variation in convergence characteristics due to the temperature variation can be reduced, the spot shape cannot be improved. Also, there is a problem that the configuration becomes complicated and thus the apparatus becomes expensive.
In the configuration disclosed by the JP 2001-126642A, it is difficult to improve the spot shape and correct the pincushion distortion of right and left rasters. Moreover, there is a problem that the configuration becomes complicated.